Screw pump

Abstract

A screw pump including a screw assembly in a sleeve, the assembly comprising a drive screw having protruding threaded sides, and multiple driven screws having concave threaded sides which are closely meshed with the drive screw, thus forming a series of sealed chamber. The screw pump further includes one or more channels which are formed in the circumferential direction around the periphery of the driven screws, so that the final sealed chamber adjacent a discharge port of the pump partially communicates with the port through the channels shortly before the chamber completely opens to the port.

What is claimed is: 
     
       1. A screw pump comprising a screw assembly including a drive screw having protruding threaded sides and at least one driven screw having concave threaded sides which are closely meshed with said threaded sides of said drive screw, a sleeve, said screw assembly being closely fitted into said sleeve and thus forming a series of sealed chambers including a final sealed chamber, said sleeve and said assembly further having an intake port at one end thereof and a discharge port at the other end thereof, and at least one circumferentially extending channel formed in the peripheral surface of said driven screw, said channel extending entirely across said peripheral surface, whereby said final sealed chamber which is adjacent said discharge port partially communicates with said discharge port through said channel shortly before said final sealed chamber completely opens to said discharge port. 
     
     
       2. A screw pump comprising a screw assembly including a drive screw having protruding threaded sides, two driven screws having concave threaded sides which are closely meshed with said threaded sides of said drive screw, a sleeve, said screw assembly being closely fitted into said sleeve and thus forming a series of sealed chambers including a final sealed chamber, said sleeve and said assembly further having an intake port at one end thereof and a discharge port at the other end thereof, and at least one circumferentially extending channel formed in the peripheral surface of each of said driven screws, said channels extending entirely across said peripheral surface, whereby said final sealed chamber which is adjacent said discharge port partially communicate with said discharge port through said channel shortly before said final sealed chamber completely opens to said discharge port, said drive and driven screws having threads, said threads of each of said driven screws having said channels formed therein, said driven screws and said channels being offset relatively to each other such that said channels connect said final sealed chambers to said discharge port at different times. 
     
     
       3. A screw pump comprising a screw assembly including a drive screw having protruding threaded sides and at least one driven screw having protruding threads forming concave threaded sides which are closely meshed with said threaded sides of said drive screw, a sleeve, said screw assembly being closely fitted into said sleeve and thus forming a series of sealed chambers including a final sealed chamber, said sleee and said assembly further having an intake port at one end thereof and a discharge port at the other end thereof, and at least one channel formed in the peripheral surface of said threads of said driven screw, said channel extending in the circumferiential direction only and does not have a substantial radial component of direction and said channel extending entirely across said peripheral surface, whereby said final sealed chamber which is adjacent said discharge port partially communicates with said discharge port through said channel shortly before said final sealed chamber completely opens to said discharge port. 
     
     
       4. A screw pump according to claim 2, wherein said drive screw and said driven screws have double threads, and said channels are formed in both of said threads of each of said driven screws. 
     
     
       5. A screw pump according to claim 4, wherein said channels of both of said driven screws are aligned in a plane which is perpendicular to the axes of said screws.